Roger makes his first appearance in the chronicles at Melfi in 1129, jointly accepting with his father and his younger brother Tancred the fealty of the rebellious peninsular barons. After his investiture as duke of Apulia in 1135, where he was perhaps put under the tutelage or guardianship of Robert of Selby, he took part in his father's campaigns there, distinguishing himself in the campaigns of 1137 against Ranulf of Alife, whom Pope Innocent II and the Emperor Lothair II had invested as rival duke of Apulia. His first major engagement was the Battle of Rignano on 30 October; a battle in which more experienced warriors, like his father, fled and some, like Duke Sergius VII of Naples, died. Roger's bravery, and success in the first charge, at Rignano solidified his martial reputation early.

After Ranulf's death (1139), Apulia was secured, but Innocent and the dispossessed Prince Robert II of Capua began to march on the prince's nominal capital. At Galluccio, Roger ambushed the papal troops with only a thousand knights and captured the pope and his entourage. Three days later, on July 25 at Mignano, Innocent confirmed the elder Roger as king, the younger as duke, and the third son, Alfonso, as prince of Capua—officially severing Robert from his support. Next, Duke Roger took the city of Naples into his possession and made it an integral part of the kingdom, ending the republican government which had continued after Sergius' death.

In 1140, after the promulgation of the king's Assizes of Ariano, the first ducats were minted bearing an effigy of the young duke in battledress beside his father, with their hands on the Cross. The ducat was named after the duchy of Apulia. Roger and Alfonso, the second son Tancred being dead, then moved into the Abruzzi to harass papal lands. At that time, late in 1140, Roger's bride to be, Isabella, arrived from the court of her father, Theobald II of Champagne. Roger's most famous consort, however, was his mistress, Emma, the daughter of Achard II, Count of Lecce,[1] with whom he had two illegitimate children, Tancred,[1] later king,[1] and William (after 1137 – 1167/68). In that same year (1140), Richard III of Gaeta died and his duchy was given to Roger.

In 1148, barely thirty, Duke Roger died an unknown death in an unknown location. He was mourned by the Arab poet Abu ed-Daw, who said, "the arms of the brave have fallen . . . and the eloquent seek for words in vain." Roger was buried in the chapel of Saint Mary Magdalene next to the old Cathedral of Palermo. He was later transferred to an eponymous chapel now in the barracks of San Giacomo. His successor was his only surviving brother, William, later king.